Until recently, the study of human prehistory relied on the material collected by archaeologists and palaeontologists. Bones, stones and pottery are not the only evidence now available to prehistorians, however: the DNA of living humans contains a record of the DNA of their ancestors. Molecular genetic techniques, developed originally in medical, agricultural and industrial research, have been seized on by scientists interested in the history of our species, and have led to spectacular advances in our understanding of human evolutionary history.
Before discussing these three popular accounts of how DNA techniques can be used to study human ancestry, I should declare an interest: I was a postdoctoral research associate in Bryan Sykes’s Oxford laboratory in the late 1980s. When I joined it in 1987, his team was working on inherited conditions such as osteogenesis imperfecta, or brittle bone disease, but my project was an attempt to recover DNA from archaeological bones, something that had not previously been achieved.
Those were exciting days. Earlier in 1987, a group of US scientists had published a paper in Nature, now considered a classic, entitled ‘Mitochondrial DNA and Human Evolution’. Mitochondrial DNA is an ideal tool for the study of evolution because it is inherited only through the maternal line, usually unchanged except for the genetic mutations that occur over time. This means it can be used to trace maternal lineages through many generations. In contrast to the bulk of the DNA carried in our cells, mitochondrial DNA is relatively uncomplicated and easy to study. The authors of the Nature report had studied the mitochondrial DNA of living people and concluded that we are all descended from a common African female ancestor, whom they called ‘Mitochondrial Eve’, or ‘African Eve’. The idea that the whole human race might have a single ancestral mother captured everyone’s imagination. Eve featured topless on the cover of Newsweek.
In the years that followed, scientists generated thousands of mitochondrial DNA sequences and used them to build phylogenetic (or family) trees, to elucidate the history of human populations. The interpretation of the data spawned an ancillary industry of mathematicians and statisticians to help classify and organise the sequences, and a pattern has gradually emerged. For example, Native American mitochondrial DNA types fall into four haplogroups (groups of similar sequences), identified by the letters A, B, C and D, which can be traced back to Asia. Polynesians, who also originated in Asia, were found to belong to mitochondrial haplogroup B. Many sub-Saharan peoples fall into subgroups of a haplogroup given the letter L.
In 1996, Martin Richards at Oxford and several other scientists, including the mathematician Hans-Jürgen Bandelt and Bryan Sykes, concluded that most of the mitochondrial DNA types of living Europeans fall into several major haplogroups, eventually named H, J, K, T, U, V and X. The paper in which they published their conclusions caused controversy because their estimated dates for the origin of the groups were at odds with accepted models of the prehistoric settlement of Europe. Later studies by Richards and his colleagues revised the nomenclature and age of the groups, and warned of the difficulties of classifying and dating mitochondrial sequences.
In The Seven Daughters of Eve Bryan Sykes fleshes out these classificatory schemes and age estimates. He gives the haplogroups names – Helena (Greek for ‘light’), Jasmine (Persian for ‘flower’), Katrine (Greek, ‘pure’), Tara (Gaelic, ‘rock’), Ursula (Latin, ‘she-bear’), Velda (Norse, ‘ruler’), and Xenia (Greek, ‘hospitable’) – and writes about them as the ‘mothers’ of all Europeans, supplying each one with a biography. Tara, for example, Sykes’s own ancestral mother, lived with her brother in a band of hunters in the depths of the last Ice Age.
Four years later she was pregnant and the first of her two daughters was born. As soon as the baby appeared it was obvious she had inherited her father’s flame-red hair. By the time she was a year old it was also obvious that she had inherited Tara’s independent streak. She refused to listen to any instructions and was always putting pebbles and even sharp flints into her mouth. Tara was a diligent mother and a welcome new member of the band. She had a good man and the hard life was as enjoyable as it could be.
The Seven Daughters of Eve has been described as a ‘boy’s own story’ that portrays its author in heroic mode, solving scientific riddles virtually single-handed, one of the ‘new boys on the block battling against the might of the Establishment’. Sykes presents several studies in human evolutionary history and promises to give the reader a sense of ‘the excitement and the frustrations of the front-line research that lies behind these discoveries. Here you will see what really happens in a genetics laboratory. Like any walk of life, science has its ups and downs, its heroes and its villains.’ The book lacks notes and a bibliography, making it difficult to verify the extent to which Sykes was personally involved in the work he describes. We do learn, however, that he drives a Mk II Jaguar/Daimler and likes Bollinger. We are also told how he solved the riddle of the origins of the Polynesians by accident, while nursing a broken shoulder (the result of a fall from a motorcycle) in the Cook Islands.
In a chapter called ‘The Tsar and I’, Sykes writes, after a cursory reference to the team that identified the skeletal remains of the Romanov family from their DNA: ‘Though I like the odd vodka, I have never considered myself a Romanov; but I couldn’t help noticing that my own DNA sequence matched that of Nicholas II.’ This isn’t as extraordinary as it might have seemed once you know that out of the several hundred people covered by the Richards study, no fewer than six, from Britain, the Middle East and northern Spain, shared the same ‘Romanov’ sequence. Indeed, hundreds of thousands of people around the world could have the same sequences as the one common to Sykes and the last Tsar, or if not the same, very similar.
Every hero’s story needs a villain, and that’s where I fit in. After I left Sykes’s laboratory in 1989, I pursued research on the analysis of DNA taken from bones. While he and his team worked on the Cook Islanders, maternal European lineages and the DNA sequence from Cheddar Man (a 9000-year-old skeleton), I applied DNA typing in a number of other cases, including the identification of the skeletal remains of the Nazi doctor Josef Mengele and the Romanovs, the evolution of the woolly mammoth, and the origins of the prehistoric Easter Islanders and other Pacific peoples. Then, a few years ago, while working on present-day populations of Melanesia, I generated data that made me doubt the exclusively maternal inheritance of mitochondrial DNA. Because the Mitochondrial Eve hypothesis depends on the premise that it is passed on from mothers alone, without recombination (i.e. without the shuffling of paternal and maternal DNA that happens from generation to generation in our chromosomes), the publication of my observations, providing almost perfect evidence of the paternal inheritance and recombination of mitochondrial DNA, caused consternation.
I eventually discovered that I had misread the DNA sequences in question. My conclusions were invalid, and I published a correction. Sykes claims the credit for my having done so, and devotes several pages of his book to describing how he ‘set the record straight’ at a scientific meeting. His version of events has me appear in the worst light, even as having deliberately withheld the truth. According to Sykes, ‘mitochondria had survived the recombination scare,’ though ‘getting to the truth had been an exhausting, unpleasant and distressing experience.’ I am at a loss to explain why a successful Oxford professor, who at one time or another has been a Parliamentary scientific adviser and a member of steering committees and funding boards, should feel that he needs to denigrate a former colleague in a popular book. The usual way to pursue scientific disputes is through peer-reviewed articles in scientific journals.
In addition to being a vehicle for self-promotion, often at others’ expense, The Seven Daughters of Eve serves as a marketing device. The dust cover of the hardback edition proclaimed that Sykes ‘has always emphasised the importance of the individual in shaping our genetic world. The website www.oxfordancestors.com offers people the chance to find out for themselves, from a DNA sample, where they fit in.’ Oxford Ancestors is Sykes’s own company, which, for a fee, will submit a sample of your DNA to a MatriLine™ DNA test so that you can find out which of the seven ancestral mothers is yours. You don’t have to be European to benefit from the service; customers will be matched to one or another of the clans so far discovered throughout the world and will receive a certificate, suitable for framing, identifying their maternal ancestor. Oxford Ancestors also offers Y-chromosome tests, so that male customers can identify their paternal lineage.
The Y chromosome – the subject of Spencer Wells’s The Journey of Man – is the genetic structure, passed from fathers to sons, that determines maleness. It is relatively large and complicated, and it took scientists quite a time to find markers suitable for its use in population genetics. Y-chromosome research is now more fashionable than research into mitochondrial DNA: after several years of Eve, we have Adam. Y data, too, support the theory that modern humans originated in Africa, but the ages obtained for Adam are much more recent: he is said to have lived only about 50,000 years ago, in contrast to Eve’s 150,000. The Journey of Man explains this discrepancy. Throughout history, relatively few men have fathered most of the children, leading to the rapid extinction of many male lineages, and thus a more recent common ancestor for those that survive today. The Y chromosome is considered a better system through which to study human evolution as, unlike mitochondrial DNA, it does not produce troublesome phylogenetic trees.
Wells explains that The Journey of Man is not intended as a sexist title: the book is literally the story of the passage of men from archaic ancestors to present-day males, traced by means of genetic analysis of the Y chromosome. It was conceived as part of a television documentary and claims to fill in the scientific background, which it does almost to excess, with lots of detail of the origin and distribution of the male haplogroups. Wells is perhaps a little uncritical, on the other hand, and exaggerates the capacity of molecular biology to understand the past: ‘Each of us is carrying a unique chapter [of our history], locked away inside our genome, and we owe it to ourselves and to our descendants to discover what it is.’ His concluding remarks threaten that ‘one responsibility that we neglect at our peril is that of self-discovery. Once the document of our journey has been lost it will, like the footprints of our ancestors as they left Africa to colonise the globe, be gone for ever.’
Sykes’s and Wells’s optimism contrasts with the more guarded tone of Mapping Human History, whose author is a science journalist. Steve Olson initially makes grand claims about genetics and how it will help relieve suffering by conquering hunger, disease and mental illness, and promises to tell a story of conflict, adventure, triumph and sex. As a book aimed at the intelligent lay reader, it is well researched, using primary sources, and contains a useful index.
Olson explains how the DNA in our cells carries a record of the transition from apes to humans in Africa, the evolution of archaic into modern humans, and their diversification into different ethnic groups. The concept of race is now regarded with suspicion by geneticists, as humans come in a continuum of colours and shapes, rather than in distinct racial groups, and the differences between most human groups seem to be the result of culture and history more than of biology. An important conclusion to emerge from research into genetic variation is that people around the world are very similar, and variation between groups mostly skin-deep. An estimated 85 per cent of genetic variation occurs within defined population groups, and only 15 per cent between groups.
Differences in the frequency of genetic markers among different groups make it possible to use genes to track developmental events. Yet the more we learn, the more clearly we will realise that genetic testing cannot define our identity. Olson tells the story of a US geneticist whose offer to trace the African origin of African-American men floundered when a third of his subjects discovered that they had European paternal ancestry.
The number of our ancestors increases exponentially, generation by generation. We may have only four grandparents, but go back a few dozen generations and we have more ancestors than the current world population. Our nuclear DNA, inherited from both parents, is a patchwork. Mitochondrial DNA might be inherited from one maternal ancestor, and the Y-chromosome DNA from one paternal ancestor, but these systems make up only a tiny proportion of our genetic heritage: they don’t define ‘who we are’ or ‘where we come from’.
Olson begins his book holding out great hopes for the power of genetics to reconstruct human ancestry, but ends it by saying that people’s identity is determined by political and historical circumstances, by their abilities, experience, social background, upbringing and choice, not by their DNA. Even in the case of the genes that predispose us to cancer, high blood pressure or adult-onset diabetes, a person with such a gene is not destined to develop the disease in question: he or she will have a statistically higher chance of developing it under certain environmental conditions.
Nevertheless, thousands of people eager to trace their roots will pay to find out whether they belong to Tara, Jasmine or Helena’s clan, or whether they have a ‘Viking’ Y chromosome. Books such as The Seven Daughters of Eve make one question the limits of acceptable popularisation, as well as the commercial exploitation of public interest in a new and exciting scientific field. Many of the ‘astonishing’ findings celebrated in popular science books should be viewed with caution. Olson’s book is the most balanced and informative of the three here. However, even he lapses into whiggishness, describing the origin of humans from the vantage point of today’s victors. Meanwhile, we still don’t know for sure whether mitochondrial DNA survived the recombination scare, or why Adam is so much younger than Eve. Debates about the interpretation of genetic data remain unresolved, and new models are being suggested to explain the human settlement of the Pacific and other parts of the world.
Scientists working on the genetic analysis of human populations deal with abstract models in order to explain genetic data, not proven historical facts. The process contains an element of doubt and is infinitely more exciting than it appears in these books. The professional stakes are high: scientific stories generate not only television programmes, but also research grants and permanent jobs. Such stories are not usually told by or about the unestablished scientist, or the one with a worthy but dull-sounding project, the modest scientist, the scientist in a developing country – or the woman scientist. Olson tries perhaps a little too hard to be politically correct, but he is to be credited for having interviewed several female molecular geneticists, including Rebecca Cann, Anne Stone, Himla Soodyall, Georgia Dunston and Batsheva Bonné-Tamir. Human evolutionary history isn’t just a boy’s own story.